The present invention relates to magnetic direction sensing systems and particularly those for use in vehicles.
U.S. Pat. No. 4,546,551 discloses a flux-gate type sensor and microprocessor controlled compass system which provides both compass compensation and variation correction for a vehicle compass. Although the system works well, it is necessary in some instances to recompensate the compass due to changes in the vehicle's reaction to the earth's magnetic field during the life of the vehicle and during its use. Thus, for example, driving a car through a car wash can flex the sheet metal in the neighborhood of the compass sensor and subsequently change the reaction of the sensor to the earth's magnetic field. With existing compass systems such as the one disclosed in the above identified patent, it is necessary to recompensate the compass at periodic intervals to correct for these variations to provide an accurate heading display over a period of time. It is noted that these problems are somewhat unique to vehicles and particularly to automobiles.
Another problem which is the subject of erratic operation of a vehicle compass is that when the vehicle travels over or near large ferro-magnetic objects such as bridges, metal buildings and the like, the heading display can and frequently will change dramatically due to the interaction of the ferro-magnetic structure with the earth's magnetic field. During such time period, the vehicle compass operation is seriously impaired and can provide erroneous heading information at an inopportune time, for example, when exiting a bridge turning lane.